"Footbridges: Small is Beautiful" (ECCE, 414pp, 2014) is a valuable addition to this particular bookshelf. It has been produced by the European Council of Civil Engineers, an umbrella body for various national groups such as the UK's Institution of Civil Engineers. It surveys nearly 200 pedestrian bridges, with over 600 photographs, covering most of Europe as well as a bonus selection from Japan.

The bridges are both ancient and modern and have been chosen for their technical, architectural or historic interest. The book is selective rather than comprehensive: for example, the eleven footbridges from the UK represent only a fraction of this country's excellent bridge heritage. Some countries are under-represented (such as Ireland, with only a single bridge included), while others are conspicuous by their absence, such as Belgium, the Netherlands, and all of Scandinavia. None of that matters given how much other interesting material the book includes.

Each chapter has a different author, and the book has been compiled rather than edited in the proper sense. Either the various writers were given different briefs, or they have disregarded them. The result is a book which is uneven in terms of depth of detail, reasons for selection of bridges, and also stylistically. Examples include the Czech Republic's chapter, which might lead the unsuspecting reader to believe that the only designer working in the country is Jiří Stráský, and article lengths which vary from the epic to the abbreviated.

Nonetheless, I found it a hugely impressive and enjoyable book. There are numerous high quality photographs, some reproduced over single and double-page spreads, and colour on every page. To get a book of this size and quality for only €29.90 (plus shipping costs) is quite amazing (order direct from ECCE).

The book opens with a lengthy chapter on the history of bridge structures, by the editor Gorazd Humar. This is useful, informative and well-illustrated. It's also idiosyncratic, with a quantity of material on Venetian bridges that goes well beyond their actual historical significance, and not one but several sections on the development of hinges in bridge structures.

The body of the book covers some 24 countries, and some truly fantastic bridges. There are some duds, but they are distinctly in the minority. Many of the photos are of exceptional quality, and really made me want to add a few new destinations to my future travel plans. Any pontist will find dozens of bridges which are new to them. The accompanying texts are for the most part aimed at the general reader, rather than at engineers or other specialists, although to be honest the book is well worth getting just for the photographs even if you don't have time to read the text.

26 December 2014

A new bridge design competition has recently been launched, for a £40m pedestrian and cycle bridge across the River Thames at Nine Elms in London. The new bridge would link Pimlico on the north bank of the river with Nine Elms on the south bank, soon to be home to the new US Embassy, as well as various other developments.

The competition website describes a three-stage process. Design teams are first requested to jump through a pre-qualification hoop, via the local authority's procurement website, presumably to weed out the chancers, no-hopers and ne'er-do-wells. There's no limit to the number of teams which then proceed to the second stage, submission of preliminary designs.

Competitors are asked to respond to five specific challenges, all of which are well chosen and show that the promoting authority, Wandsworth Council, has given serious thought to the project. The challenges include how to accommodate pedestrian and cycle traffic while providing a happy experience for both, how to achieve sufficient navigational clearance over the river while avoiding lengthy approach ramps, and how to tie the bridge in effectively to the public realm at either end.

Some of the stated aspirations for the bridge are at odds with each other. Take, for example, the first two:

Be innovative and memorable and challenging previous interpretations of bridge design

Be of an appropriate design

Is it right that an appropriate design is one which "challenges previous interpretations" of bridge design? Not only must the cake be had, it must also be eaten, apparently. An interpretation-challenging cake, innovatively made from snake's eggs and hyperflour, perhaps. That would certainly be memorable.

Entries will be judged by a jury panel featuring, amongst others, engineer Henry Bardsley, who has been involved in a few innovative bridges in his time, and architect Graham Stirk, whose practice was responsible for the Neptune's Way bridge debacle in Glasgow.

The contest does not seem to be anonymous, raising the prospect that the jury or promoter may be influenced by the names attached to entries: the desire to be associated with the Fosters and Hadids of the world rather than the Bloggs or Joneses. The promoters are open about the fact that they are not just looking for a design, but for a design team who are creative, can communicate, and have the capacity to deliver a complex and challenging project.

Following evaluation of the second stage entries, three or four teams will be selected to proceed to the final stage, developing their proposals in closer consultation with stakeholder and community groups, and each receiving a £12,000 honorarium, which is better than a slap in the face with the proverbial wet kipper, but hardly sufficient recompense for the hard work likely to be involved.

This will be an interesting competition to watch: it should attract many enthusiastic entrants, some prominent designers, and the very real difficulties of the site should lead to a number of interesting responses.

I commented on this fiasco-in-the-making last month, noting that its progress now seemed unstoppable, short of the unlikely scenario of the bridge's designers suddenly realising their own folly in an "Oh my goodness, what have I done?" moment, and deciding to quit.

This is a bridge, let's recall, which at £175m has a price tag grossly in excess of what even Donald Trump could consider reasonable (indeed, it's perhaps a surprise that Trump isn't involved, offering copious sponsorship in return for adding a couple of par-3 golf holes to the bridge). This puts it well beyond the realm of the most expensive pedestrian bridges ever built, by a considerable multiple. Having initially promised that no public funding would ever be provided, Johnson and partner-in-crime George Osborne then each offered £30m of taxpayers cash to underwrite the job.

The rest of the funding has to come from private sponsors, and so much is required that this supposedly public oasis will be converted twelve times a year into a private garden party for the use of its wealthy benefactors. Perhaps the capital city's poor and hungry can swim beneath the bridge on such occasions in the hope that some crumbs may spill from the lavishly decorated table. For the rest of the year, the bridge will be closed at night, forbidden to cyclists, and large groups (of 8 or more people) will be obliged to sneak across hoping they can dodge the inevitable CCTV hidden behind cherry blossom. For a bridge supposed to offer a great experience for the public, it won't even be a public right of way.

The bridge will ruin views along and across the Thames, including of St Paul's Cathedral, who have joined an ever-lengthening list of people who have woken up to the bridge's adverse impacts. It's neither a very good garden (central London being already well-provided with large public parkland), nor a very useful bridge, serving no genuinely worthwhile transport need. As the Guardian has recently noted, it turns the Thames into a playground for private fantasies, not public benefit.

Even bridge engineers, never an outspoken lot, are lining up to critique the proposals. Bridge expert Simon Bourne (not a fan of extravagance) was cited in the New Civil Engineer magazine stating that a decent bridge could be built for just £50m, a snip compared to the bill for the Garden Bridge. That certainly sounds reasonable, given that the structurally challenging Millennium Bridge cost about £23m just over a decade ago, and that between £26m and £40m is anticipated for the new pedestrian bridge planned at Nine Elms (of which, more another time).

In the latest New Civil Engineer, the Garden Bridge Trust's Paul Morrell responds to Bourne's criticism. Morrell is a Big Cheese, formerly the government's Chief Construction Adviser. However, his defence of the Garden Bridge illustrates everything which is wrong with this scheme.

Morrell says: "I could ask for the breakdown of [Bourne's] estimate of £50m so we can learn from it", which would seem a complete waste of time given that we already have well-established benchmark costs for pedestrian bridges over the Thames. However, a failure to benchmark costs against comparable projects is entirely normal for those whose infatuation with grandiosity triumphs over common sense.

Morrell goes on to note that £50m wouldn't even cover the Garden Bridge's non-construction costs (fees, fund-raising, land, compensation and "a long list of issues that you really do need to be working on the project to understand"). This patronising contempt for transparency is startling, but not as startling as learning that well in excess of £50m is required before you even start building the bridge - this is really quite disgraceful, but typical of a Grand Projet culture where there is little or no meaningful challenge regarding value for money.

Of course, Morrell is a quantity surveyor, a man who knows the price of everything and the value of nothing. Notably, declarations of the value of the Green Bridge have been largely poetic rather than economic in nature: hello trees, hello flowers, hello sky. The government's own guidance for public investment, the Treasury's Green Book, is routinely ignored by political promoters of the extravagant, as it requires benefits, however nebulous, to be properly evaluated and judged against the investment required. With the Garden Bridge, the net benefit may in fact be negative, and it's no surprise that no assessment of the bridge's actual value has been undertaken or published. Morrell ought to know this, so his mis-direction in justifying his project's exorbitant cost is particularly depressing.

Morrell claims: "There is always something cheaper if that is your main aim in life, but it would not get consent, nor would it be fundable, and nor would it deliver what this bridge is designed to be: a unique celebration of British talent and creativity, of design and horticulture, of this great city - and of engineering".

Again, this is just rhetorical sleight-of-hand. We are not obliged to celebrate any of these, and certainly not to divert public money in order to do so at a time when increasing numbers of our population are unable to afford to feed their families properly. Given the other pedestrian bridges which have been built over the Thames or which are planned, it's perfectly clear that a bridge can be built which offers genuine value, at a lower price, which can get consent, and for which funding can readily be obtained, if only the political will permits. Morrell, dazzled by his association with celebrity, seems unable to see that every penny spent on the Garden Bridge folly diverts resources from transport links which would serve genuine need elsewhere in the city.

The sense of defensiveness and the deaf ear to criticism and challenge is deeply reminiscent of two other architecturally extravagant bridge follies from recent times. Sunderland's ill-fated River Wear Bridge was also widely criticised, and as with the Garden Bridge, its backers misrepresented public opinion and ploughed on regardless, wasting millions of pounds of public money in the process. Simon Bourne was one of the critics on that occasion, as well. Glasgow's Neptune's Way farrago was a similar example: an absurd and rightly-criticised design which could not, in the end, be afforded, and was ditched in favour of an economic design serving the same purpose without the pointless showing off.

There is some hope that the bridge may yet be put to the sword before too much money is wasted. There's a suggestion that lawyers may seek a judicial review of the planning decisions. In addition, one of the planning conditions imposed by Westminster is that Transport for London must underwrite the future maintenance costs of the bridge (several million pounds every year). Opponents of the project are hoping that this may yet scupper the plans, Mayor Boris Johnson has confirmed that TfL have no intention of underwriting the maintenance.

03 December 2014

This bridge was another early morning visit, to an award-winning span which is probably unique in Britain.

Built in 2009 for £2.4m, the 55m long bridge is a rare all-stainless steel structure. It was designed by Price & Myers with Níall McLaughlin Architects, and built by M-Tec. You'll see it described on the internet as a "stressed skin" bridge, to make it sound like it's using aircraft technology, but to bridge engineers it's simply a twin half-through box girder bridge, conventional enough except for the geometry and material.

The two edge girders hold up the bridge and also double as parapets. They consist of continuously welded, perforated Duplex 2250 stainless steel plate (supplied by Outokumpu), wrapped around triangular diaphragms. A series of cross-beams and bracing frames are hidden within the deck, which is surfaces with perforated stainless steel planks (of which, more later). The entire bridge weighs about 75 tonnes, and sits on four hidden stub "legs", one at each corner.

The extensive use of stainless steel is a bold, and presumably expensive, choice. The bridge's skin is punctured with thousands of small holes, arranged in size according to the calculated level of stress at each point of the girder surface. The process of analysing the bridge, determining acceptable levels of perforation, and translating that back into a fabrication model, will have been complex and demanding, and is an impressive achievement.

Luminaires are located within the girders and below the bridge's floor, and the perforations allow the structure to glow from within at night.

The bridge won the IStructE Structural Award for pedestrian bridges in 2010, and I think justifiably so, as it is highly innovative and geometrically challenging. I haven't seen it illuminated at night, but in daylight, sunlight reflects off the skin in a very attractive manner. However, the bridge is not without its critics.

The main complaint appears to relate to the deck panels, which are clearly very slippery, to the extent that the bridge is disfigured by prominent warning signs at each end advising users to cross with care. Reportedly, bridge users who do slip and fall have frequently been injured by the "cheesegrater" quality of the decking. In one month, over 600 people signed a petition asking for the bridge decking to be replaced.

However, as with the nearby Valentine Bridge, this is a public amenity which is privately owned. Although the decking is clearly not fit for purpose, the public may find it hard to force change.

25 November 2014

I'm nearly caught up on a backlog of bridge visits. The next two are both in Bristol, where I've previously covered Clevedon Pier (yes, I know that stretches the definition of "Bristol" and "bridges") and Pero's Bridge.

Valentine Bridge was built in 2000 by Alfred McAlpine, to a design by Atkins. The steel cable-stayed bridge carries pedestrians and cyclists across Bristol's Floating Harbour close to Temple Meads railway station.

As with the nearby Meads Reach footbridge (for which, see the next post), the bridge was privately funded and is privately owned.

The structure is S-shaped in plan, with a triangular cross-section framed truss deck. The upper and lower chords are circular steel tubes, connected by I-section struts in a Vierendeel arrangement.

This is not a good bridge.

It seems evident that the client must have wanted a "landmark" bridge of some sort, hence the mast, cables, and general layout. However, little effort seems to have been put into creating an efficient or well balanced structure. Of the four back-stay cables, two are so slack as to appear un-stressed, presumably a result of a cable layout which appears baffling when viewed from overhead. A balanced layout could have been achieved with fewer cables working more effectively.

Some of the cable detailing also looks a little awkward, perhaps cheap, especially the anchor detail to the deck.

The curved stainless steel parapets seem to be trying a little too hard, with an over-pronounced arc to the parapet posts. The abutment at one end, a mix of bold brick and prison-fencing (to guard the bearings), is quite unfriendly, as are the (pointless) anti-cycling barriers which block the walkway entrance.

Most annoying of all is the decking, which seems to have been fixed incorrectly, making a pronounced clattering sound each time someone crosses the bridge. If you watch the video below carefully, you can see the deck planks actually bouncing up and down.

21 November 2014

Bridges in Slovakia (Jaga, 272pp, 2014, also available in Slovak) [amazon.co.uk] is a lavish coffee table gazetteer, a real labour of love, and a book I would unreservedly recommend to Pontists everywhere.

Peter Paulík is a Slovak engineer who spent roughly two years touring his country, photographing, researching and writing this book. The result is a very well-produced effort, well designed and with large, full-colour photographs and diagrams on almost every page. You can get a good idea of the content without buying the book, as Peter has made the whole book available entirely free of charge in PDF format.

Amazon are currently listing this book, but I think it's best to buy directly from Peter online, the cost is only €36 including postage (in Europe), which is astonishingly cheap for such an large and well-illustrated volume.

The book opens with a series of prefaces and introductions, of which Paulík's short account of his bridge-hunting expeditions is the most interesting - he has braved real difficulties to locate and photograph some of the structures. There's also a good introductory guide to types of bridges, with very clear diagrams, some statistics on the number and type of bridges in Slovakia, a timeline and list of particularly significant structures.

The main section of the book is the gazetteer, arranged alphabetically by location. This covers all types of structures, from all periods of construction. Each bridge has a photograph or historic illustration, map coordinates, and explanatory text. Some structures are accompanied by further photographs and extracts from technical drawings.

Many of the bridges are relatively ordinary, but there are many which are beautiful, unusual and interesting. Major structures are given more attention and space. The photographs are generally of a
very high quality.

For anyone with a particular interest in Slovakia's architecture or infrastructure, this is an essential book. For other bridge enthusiasts, it is still a very enjoyable and informative tome. I think most of the bridges are little known outside their own nation, but many deserve wider attention. There are some gorgeous masonry arch structures; oddities such as a wooden "ecoduct", a bridge made from an old railway carriage, and an airport runway lighting bridge; and hosts of intriguing bridges in modern materials. As well as the masonry spans, I particularly like a number of small suspension bridges and pipeline structures.

Hopefully the book will bring the rich heritage of bridge design and construction in Slovakia to much wider attention.

Léon Blum Viaduct Bridge / RFR"We have chosen to create a structural continuity between the bridge deck and its vertical supports which are articulated at their base. In doing so, the area of the bridge which is most directly in contact with the town is freed from the kind of massive support commonly associated with this type of Bridge."

18 November 2014

Marc Mimram has beaten seven other teams to design a new €60m highway and tram bridge over the Danube in Linz, Austria. The other competitors included heavyweights such as Leonhardt Andra, Flint and Neill, Knight Architects, Dietmar Feichtinger and Dissing + Weitling.

It's a big bridge, some 30m and 400m long in total, and it's perhaps surprising to see a winner which is an essentially entirely new type of bridge. Essentially, it's a steel cantilever bridge along the lines of the Forth Railway Bridge, but with a number of unusual features.

The cantilever trusses are curved rather than comprised of straight pieces, requiring significant quantities of additional steel to resist the local bending induced in the steelwork. Very limited support is provided to the deck, which therefore has to be excessively deep.

The oddest feature, however, is the fact that the cantilevers sit on single lines of bearings, so that under uneven loading, the only stability is provided by the connection between adjacent cantilevers. Those short connection pieces don't really look stiff enough to provide that stability, and I wonder quite how the engineer has persuaded the design to work.

Of the other designs, the 4th prize entry is the most ambitious, with what appears to be a 250m span network arch bridge (just shy of the existing longest span of this type), a very challenging and complex structure to build.

17 November 2014

Love it or loathe it, the world's most expensive pedestrian bridge has now secured half of the planning consent that it needs to go ahead. Of course, I loathe it. It's an utterly disgraceful waste of public money in a location which doesn't need another tourist attraction, nor need to be the site of a bridge which would permanently wreck the London riverscape.

What's clear about the Garden Bridge is how the cult of celebrity provides a comfort blanket allowing people to suspend their normal critical faculties. It's got Heatherwick, it must be good. Joanna Lumley likes it. It seems clear that, short of hoping for the bridge to fail to secure the necessary funding or to come in way over-budget once it reaches construction tender stage (both being quite realistic possibilities of course), the only way to put a stop to this fiasco is for the designers themselves to wake up to the realities of their iconic fantasy, do the decent thing, and quit.

15 November 2014

This is the final bridge in this series of posts about the bridges of southern France.

What can I say about the mighty Pont du Gard, justly the most famous of the surviving Roman aqueducts, a magnificent bridge, a World Heritage Site, a gorgeous, golden-hued monument to the achievements of antiquity?

I'll try to avoid the obvious: there are plenty of websites and books, linked at the bottom of this post, which will tell you all you need to know about how big it is, when it was built, and why.

A few thoughts:

The site of the bridge is well looked after. An exhibition is tucked well away from the river gorge, and a cafe and restaurant are both a discrete distance away from the bridge. It's a great spot to picnic, and to swim in the river.

The arches on the lowest tier are each built in four parallel sections, and those of the middle tier in three parallel sections, all without any mortar (only the top tier was built with mortar). I noted the same feature at the Pont d'Avignon, and presumed it allowed the builders to reuse the timber centering multiple times. That first ring of massive stone blocks would have felt pretty precarious, though. Paillet's paper on the bridge (linked below) suggests instead that the centering was for the full width of the bridge, and the parallel sections were just adopted to simplify the size of blocks that the masons had to be cut, making all the voussoirs identical. I'm not entirely convinced by this argument.

There are a multitude of projecting stones on both the side faces of the bridge and the support piers, but also, more unusually, within the arch barrel itself. These were normally used on arch bridges to provide support to the temporary timber centering. I don't think I've ever encountered corbels in the arch barrel itself before. Is this a common feature on Roman bridges?

The lowest tier of the bridge was extended in the mid-18th century, creating a new highway bridge parallel to the Roman bridge and butting up against it. Some effort was made to make this similar to the older bridge, but the stonework is very different, as are the cutwaters. Most noticeably, the old bridge is level, but the new bridge is ramped up towards its centre point, seriously spoiling the appearance of the bridge from both sides. It's no surprise that most "postcard" views of the bridge are therefore taken from the unaltered elevation.

More positively, the extension bridge does allow people to appreciate the monument from close up, without exposing it to the deterioration that would inevitably result if large numbers of people were encouraged to clamber upon it.